Filament for incandescent lamps and process of manufacturing same



UNrrsn STATES.

PATENT OFFICE.

THOMAS A. EDI-SON, or LLEWELLYN PARK, NEW JE SEY.

FILAMENI FOR INCANDESCENT LAMPS AND PROCESS OF MANUFACTURING SAME.

- SPECIFICATION forming part of Letters fatent No. 626,460, dated June 6, 1 899.

' Application filed Karol: 31, 1898. Serial No. 876,981. (No specimens.) I

1'0 all whom it may concern:

Be it known that l, THOMAS A. EDISON, a citizen of the United States, residing'at Llewellyn Park, in the county of Essex and State of New Jersey, have invented a certain new andgizseful Improvement in Filaments for Incandescent Lamps and Processes-of Manufacturing the Same, (Case No. 995,) of which the following is a specification.

My invention relates to an improved fila ment for incandescent lamps which will be of a high resistance, and hence suitable for use on high-tension currents, and to an improved process for the prod uctionpf such filaments.

In carrying out my invention I form a filamenhof highly-refractory non-conducting material whichis preferably porous, and incorporate therein isolated particles of carbon-,- soas to produce spark-gaps between the parti-' cles, whereby hign-tcnsion currents, either alternating, continuous, orintermittent, will be conducted from particle to particle of the carbon to raise the filament to incandescence. By constructing the filament of a highly-refractory non-conducting porous material the interior thereof will be subjected to the effect of the vacuum to thereby assist in the com duction of the current through the carbon particles. The highly-refractory material which I prefer to use in the formation of my improved carbons is an oxid or'oxids of the rare earths-such as the oxid of zirconium, tho.- rium, and others-and I prefer to incorporate therein the isolated particles of carbon by a process of carbonization.

In order to provide an'exterior surface for the filament which will radiate light, I pref erably momentarily dip the filaments in a salt of the oxid, such as the acetate thereof, which will leave no carbon upon carbonizetion.

In making my improved filaments I prefer to admix with a highly-refractory non-conducting material, such as the oxid of zirconium or thorium, a carbonizable organic compound-such as. a solution of sugar, asphalt, ora tartrate of the oxid itself-which will save a residue of carbon upon carbonization.

he proportion of carbonizable material admixed with the refractory substance depends upon the amount of carbon residuum desired to accommodate the filaments to the tension of current employed. The carbonizable material having been incorporated with the oxid orother'refractory non-conductingsubstance, the plastic compound is preferably forced by heavy pressure through a fine opening or die to form a filament of the desired cross-sectional area. The filament is then bent into the proper shape and is carefully dried, after which it is carbonized in any suitable way.

The body of the filament will be dark in color, and hence will not give the desired high economy of radiation. It is therefore preferable to immerse the filament after drying, butbefore carbonizatiomin some substance of a sufficiently-refractory non-conducting nature which will leave no carbon upon carbonization, but which will result in the production of a white coating of high radiating capacity. by preference obtained by dipping the filaments after drying, but before carbonization, in a salt of the oxid of the rare earths, such This coating of high radiation is i as zirconia or thoria, and preferably inan acetate of such oxid. A filament produced in this way will be composed largely of the refractory non-conducting material, with isolated particles of carbon therein. I Owing to,

its resistance it cannot, therefore, be satisfactorily used on ordinary currents; but when alternating, continuous, or intermittent currents of several hundred volts are directed to the platinum terminals to which the filament is secured and the bulb exhausted in the ordinary manner the tension will be sufiicientto produce a semiconduction, which results in the generation of enough heatin the internal portion of the filament to bring it up to incandescence;

Instead of carrying out the im proved process above outlined the filaments may be formed by forcing through a die or-otherwise producing the filament of plastic masses of a salt or salts of the oxidsui-nd by then subjecting the filaments to heat sufficient to decompose-the salt of the osid to result in the production of too the desired white surface and are then car-- bonized':

Instead of producing the improved filaments oy manipulating masses of the desired refractory non-conducting material, as explained, decomposable salts of -the oxids of the rare earths can be formed into filaments of the desired shape and size by a series of heating operations, which will result in the gradual accumulation of the oxid or oxids.

For example, threads of cotton "may be soaked in a salt of the oxid, such as the acetate, and carbonized to form a deposit of the oxid therein, being resoaked and reheated successively until the desired quantity of oxid has been deposited, after which the filament will ,be soaked in the desired carbonizable substance, and after being dried'will be dipped in a solution of a salt of the oxid to form' the white radiating-coating desired, and finally carbonized. 7

Having now. described my invention, what- I claimas new, and desire to secure by Letters Patent, is as follows 1. An improved filament for incandesce'n lamps, consisting of a highly-refractory, nonconducting material,having isolated particles of copductingmaterial therein, substantially as set forth.

2. An improved filament for incandescent lamps, consistingof a highly-refractory, non- 1 5. An improved filament for incandescent lamps, comprising a highly-refractory, nonconducting oxid 'or oxids of the rare earths, isolated particles of carbon therein, and a white refractory, non-conducting radiating .coating for said filament, substantially as set .forth.

6. An improved filament for incandescent lamps, comprising a highly-refractory, nonconducting oxid or oxids of the rare earths, isolated particles of carbon therein, and a white radiating coating of such oxid, substantially as set forth.

7. An improved process for making highresistance carbon filaments, which consists in forming the filament of highly-refractory,nonconducting material mixed with a carbonizable substance, which when carbonized .will deposit isolated particlesof carbon, and in fiarblpnizing thefilaments, substantially as set ort Y 8. An improved process for making highresistance carbon filaments, which consists in forming the filaments 'ofa highly-refractory, non-conducting substance with which is mixed a carbonizable material, which when carbonized will deposit isolated particles of carbon, in drying the filaments, and in finally car bonizing the same, substantially as set forth,

,9. An improved process for making-high. resistance carbon filaments, whichconsists in forming the filaments of a highly-refractory non-conducting snbstancewith which is mixedacarbonizable material, in drying the filaments,in dipping the same in a salt of a highlyrefractbrymon-conducting oxid, and in finally carbonizing the same, substantially as set forth. This specification signed and witnessed this 29th day of. March, .1898.

\ THOMAS A. EDISON. Witnesses: J. F. RANDOLPH, JNo. R. TAYLOR. 

